DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS

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DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS

• Dr. Waseem Bahjat Mushtaha
• Specialized in prosthodontics

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1- dental articulation

• Dental articulation
• It means the contact relationships of maxillary
  and
• mandibular teeth as they move against each other.
  This is a dynamic process.
• Articulator
• It is a mechanical instrument that represents the
  tempomandibular joints and jaw members, to which
  maxillary and mandibular cast may be attached to
  simulate some or all-mandibular movements.
• Occlusion
• It is the static relation ship (process of
  closure) between the incising or masticating
  (occluding) surfaces of the maxillary and
  mandibular teeth when they are in contact.

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• Centric occlusion
• It is the relation of opposing occlusal surfaces
  which provides the maximum planned contact and\or
  intercuspation.
• Centric relation
• It is the relation of the mandible to the maxilla
  when the condyles are in uppermost and rearmost
  position in the glenoid fossa at a given degree
  of vertical dimension (jaw separation). This
  position may not be recorded in the presence of
  dysfunction of the masticatory system.
• Centric occluding relation
• It is a term sometimes used to describe the
  condition in which the jaws are in centric
  relation and the teeth or occlusal surfaces in
  centric occlusion.

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• Anatomical articulation
• It is an occlusal arrangement where the posterior
  artificial teeth have masticatory surfaces (can
  make normal masticatory movements with comfort
  and efficiency) that closely resemble those of
  the natural healthy dentition and articulate with
  similar natural or artificial surfaces.
• Balanced occlusion
• It means that the artificial teeth are set up so
  that as many teeth as possible are in occlusion
  in any occlusal relationship.
• Balanced articulation
• It is bilateral, simultaneous, anterior, and
  posterior occlusal contact of teeth in centric
  and eccentric positions. It means an arrangement
  of the teeth so that in any occlusal relationship
  as many teeth as possible are in occlusion, and
  when changing from one relationship to another
  they move with a smooth, sliding motion , free
  from cuspal interference and maintaining even
  contact

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• Curve of Spee (anteroposterior curve)
• It is the anatomic curve established by the
  occlusal alignment of the teeth, as projected
  onto the median plan, beginning with the cusp tip
  of the mandibular canine and following the buccal
  cusp tips of premolar and molar teeth, continuing
  through the anterior border of the mandibular
  ramus, ending with the anterior most portion of
  the mandibular condyle
• Curve of Menson
• It is the curve of occlusion in which each cusp
  and incisal edge touches or conforms to a segment
  of the surface of a sphere 8 inches in diameter
  with its center in the region of the glabella

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• Curve of Wilson (mediolateral curve)
• It means in mandibular arch, that curve , as
  viewed in frontal plane, which is concave
  inferiorly and contacts the buccal and lingual
  cusps of the mandibular molars. In the maxillary
  arch, that curve, as viewed in frontal plane,
  which is convex superiorly and contacts the
  lingual and buccal cusps of the maxillary molars.
  The curved is formed by the facial and lingual
  cusp tips on both sides of dental arch
• Compensating curve
• It is anteroposterior curvature (in the median
  plane) and the mediolateral curvature (in the
  frontal plane) in the alignment of occluding
  surfaces and incisal edges of artificial teeth
  that are used to develop balance articulation.
  These curves introduced in the construction of
  complete dentures to compensate for the opening
  influences produced by the condylar and incisal
  guidance during lateral and protrusive mandibular
  excursive movements, these curves are artificial
  counterparts of the curve of Spee and monsoon,
  which are found in the natural dentition.

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• The working side
• It is the side on which the chewing is being done
  at the movement it is the side to which the
  mandible has moved.
• The balancing side
• It is the side opposite to the working side. It
  is the side on which, although there is greater
  separation of the teeth, there is at least one
  point of contact between the upper and lower
  teeth. It is also the side on which the grater
  condylar movement has occurred

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II-FACE-BOW

• Def the face-bow is a caliper-like device that
  is used to record the relationship of the jaws to
  the temporomandibular joints or the opening axis
  of the jaws and to orient the casts in this same
  relationship to the opening axis of the
  articulator.

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Types of face-bow

• 1-the arbitrary (maxillary) face-bow
• 2-the kinematic (mandibular, hinge axis locator)
  face-bow

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1-the arbitrary (maxillary) face-bow

• A-The maxillary face-bow is one generally used in
  construction of complete denture
• B-it is used to record the position of the upper
  jaw in relation to the hinge axis and
  transferring the relation to an articulator.
  The maxillary face-bow is simple to use and
  relatively accurate, and is based on
  average computations of an axis
  opening of the jaw.

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• C-it is placed on, the face with condyle rod
  located
• approximately over the condyles.
  
• D- The condyle rods of one particular model are
  positioned on a line extending from the
  outer canthus of the eye to the top of
  the tragus of the ear and approximately 13mm
  in front of the external auditory
  meatus. The rods of another commonly used
  model (ear face bow) are designed
  to fit into the external auditory
  meatuses (as a posterior reference point).
• E-the fork of maxillary face bow is attached to
  the maxillary occlusion rim so the record is
  a simple measurement from the jaws to the
  approximate axis of the jaws.

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2-the kinematic (mandibular, hinge axis locator)
face-bow

• A-it is used to locate the true terminal hinge
  axis and transfer this record to the
  articulator when mounting the maxillary
  cast. However, use of it can aid in recording
  centric relation.
• B-the fork of kinematic face-bow is attached to
  the mandibular occlusal rim.
• C-since this is used to orient the casts on an
  articulator in the same relation to
  the opening axis of the articulator as the
  jaws are to be the opening axis of jaws

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Functions of a face-bow

• 1-locate the terminal hinge axis by the use of
  kinematic face bow.
• 2-relate the maxillary cast to the transfer axis
  of the articulator in the same relationship as
  the maxilla is related to the mandibular hinge
  axis.
• 3-relate the mandibular cast to the hinge axis by
  means of a centric relation record.

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• An arbitrary mounting of the maxillary cast
  without a face-bow transfer can introduce errors
  in the occlusion of the finished denture. A face
  bow transfer is essential when cusp teeth are
  used, allows minor changes in the occlusal
  vertical dimension without having to make new
  maxillo-mandibular records, and is also most
  helpful in supporting the maxillary cast while it
  is being mounted on the articulator.

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ARTICULATORS

• DEF is a mechanical device which represents the
  temporo-mandibular joint and jaw members to which
  maxillary and mandibular casts are attached to
  simulate jaw movements. The records made with
  occlusion rims are used to mount the master casts
  and to adjust to articulator. They also help in
  maintaining the desired jaw relationships of the
  casts during setting up of teeth.

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Articulators are classified according to the
instrument capability and record acceptance into

• 1-simple hinge articulators.
• 2-mean value or fixed condylar path articulators
• 3-adjustable condylar path articulators
• A-semi-adjustable articulators.
• B-fully adjustable articulators.

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1-simple hinge articulators or plain line
articulators

• 1-They are cold plain line articulators since
  they only permit vertical motion i.e. simple
  opening and closing or hinge-like movement
• 2-they accept a single interocclusal record,
  which is the centric occluding relation record.
• 3-Gariot's articulator is a representative for
  this type of articulator. It consist of upper and
  lower members joined by a simple hinge with a set
  of screw against a metal plate posteriorly to
  serve as a vertical stop to increase or decrease
  the distance between the two members of the
  articulator.

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2-mean value or fixed condylar path articulators

• 1-these articulators accept single interoclusal
  record the centric occluding relation
  record, they permit horizontal as well as
  vertical movements. Eccentric movements
  permitted are based on average value. For
  many patients the condylar path ranges from
  30-40 from the horizontal with an average 32.
  The inclination of the condylar guidance of
  the articulator is fixed to the average value
  and cannot be adjusted in any manner.

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• 2-Gysi articulator, Mahdy articulator and
  Artek.pro are representive of these types of
  articulators. They consist of upper and
  lower members which are joined by two vertical
  posterior posts "condylar post
  support" fixed to the lower member,
  whereas the upper end of each post has an
  inclined groove representing the condylar
  path, through which the condylar shafts,
  extending from the upper member are
  located and moved in this groove allowing
  horizontal movement of the upper
  member.

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• 3-anterior vertical post, "the incisal post"
  which is attached to the upper member of the
  articulator by a screw , while its lower end
  rests on an inclined table, "the incisal guide
  table" which is fixed to the lower member of the
  articulator.Inclination of the incisal guide
  table is fixed at about 30 from the horizontal
  plane.
• 4-in the incisal post there is a hole, through
  which the incisal pin passes. The tip of this pin
  is designed to touch the midline of the occlusal
  rim labially.

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• 5-in Gysi articulator, the upper cast is mounted
  according to Bonwill's triangle which is
  a four inch (10 cm) equilateral triangle
  extending poseriorly from one condyle
  to the other and joining the lower
  incisor's contact point
  anteriorly. While the lower cast is mounted
  according to the recorded centric occluding
  relation record.
• 6-in Mahdy articulator and Artek pro articulator
  face-bow transfer is used to mount the
  upper cast while the lower cast is mounted on
  this instrument using centric
  occluding relation record.

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3-adjustable condylar path articulators

• This type of articulators differ from the fixed
  condylar path articulators in that they can
  accept eccentric records which are used to adjust
  the condylar guidance of the articulator, so that
  the movements of its jaw members closely resemble
  that produced by the patient. According to the
  eccentric records accepted by these types of
  articulators they are classified into
• A-semi adjustable articulators
• B-fully adjustable articulators

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A-semi adjustable articulators

• This type of articulators can accept the
  following records
• 1-face-bow record to mount the upper cast.
• 2-centric occluding relation record to mount the
  lower cast.
• 3-protrusive record, to adjust the articulator's
  horizontal condylar guidance that
  corresponds to the patient's horizontal condylar
  path inclination. Where as the articulator
  lateral condylar guidance is adjusted according
  to the Hanau's formula
• Hanau's formulaLH\8 12
• Lthe lateral condylar path inclination.
• Hthe horizontal condylar path inclination

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B-fully adjustable articulators

• This type of articulator can accept the following
  records
• 1-face bow record to mount the upper cast.
• 2-centric occluding relation record to mount the
  lower cast.
• 3-protrosive record, to adjust the articulator's
  horizontal condylar guidance which
  corresponds to the patient's horizontal condylar
  bath inclination.
• 4-right lateral record, to adjust the left
  lateral condylar guidance which
  corresponds to the patient's lateral
  condylar path inclination.
• 5-left lateral record, to adjust the right
  lateral condylar guidance which
  corresponds to the patient's right
  lateral condylar path inclination.

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Indexing the cast

• Indexing casts prior to mounting them on an
  articulator permits removal of the cast and
  accurate replacement to the articulator. Indexing
  is also important for remounting procedures made
  for correcting occlusal errors after curing a
  denture. Indexing can be accomplished by placing
  grooves or notches, in the cast or by using
  remounting plates

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Mounting the master cast on the articulator

• In the process of mounting master casts on a
  fixed condylar path articulator the following
  steps should be performed
• 1-the upper and lower casts are prepared for
  laboratory remount by cutting indices on the
  under surface of both casts. These indices
  are protected by tin-foil.

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• 2-the upper and lower trial denture bases are
  sealed with wax to their casts, thus the upper
  cast, lower cast and wax rims are all attached
  together. The arms of the articulator to be used
  are lubricated with Vaseline or oil to facilate
  cleaning the articulator from the plaster after
  the case is finished.
• 3-the incisal guide pin of the articulator is
  adjusted until its top flushes with the top of
  the upper member.
• 4-a rubber band is placed on the articulator,
  extending from the lower mark of the
  incisal
  guide pin and around each condylar post support.
  
• Adjust the rubber band to form a plane that
  divides the space between the upper and lower
  members of the articulator equally "Bonwell
  triangle"

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• 5-Three lumps of modeling clay are placed on the
  lower mounting plate to serve as an adjustable
  cast support
• 6-with the base plate and occlusion rims sealed
  together, place both maxillary and
  mandibular casts in the correct
  relationship on the three clay supports in the
  articulators .then align them until of the
  occlusal plane of occlusion rim is parallel to
  the plane established by the rubber band
• 7-open the articulator, and paint the base of
  maxillary cast with a separating medium.

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• 8-mix, and add plaster to the base of the cast
  and to the upper member of the articulator.
• 9-close the articulator until the incisal guide
  pin touches the incisal guide table and
  then add more plaster as needed to fill any
  voids.
• 10-after the stone has set, invert the
  articulator, and open it. Removing the
  modeling clay cast supports, paint
  separating medium on the base of the lower cast
  and attach it to the articulator with plaster.
• 11-permit the plaster to set, then remove excess
  plaster with a knife.

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Occlusion rims

• An occlusion rim is a wax form used to establish
• 1-the proper lip and cheek support (fullness of
  the lips and cheeks)
• 2-the arch form, which is related to the activity
  of the lips, cheeks and tongue.
• 3-the level of the occlusal plane.

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• 4-accurate maxillo-mandibular jaw relations i.e.
  Help to determine
• A-vertical dimension and an estimate of the
  interocclusal distance.
• B-horizontal jaw relations (centric occluding
  relation and condylar path)
• 5-occlusion rims help to determine the length and
  width of the artificial teeth
• A-high and low lip lines are used for determining
  the length of the artificial teeth.
• B-canine line i.e. corners of the mouth the
  distance between the canine lines determines the
  width of the six anterior teeth.
• C-the distance between the canine line and the
  posterior end of the occlusion rim determines the
  mesiodistal width of the posterior teeth.
• 6-position of midline of the arch for the correct
  placement of the central incisors.
• 7-arrangement of the artificial teeth to the
  trial denture (setting up of the teeth).

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• Base plate wax is the most commonly used occluasl
  rim material. Compound and a mixture of the
  plaster and pumice are sometimes used for
  constructing occlusal rims. There are four basic
  factors that should be considered in the proper
  fabrication of occlusion rims, to assist the
  dentist and the dental laboratory technician
  throughout the many phases of denture
  construction.

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• These factors are
• 1-relationship of natural teeth to alveolar bone
• Since the final goal in the treatment of the
  edentulous patient is to provide a functional and
  esthetic prosthesis, the relationship of the
  natural teeth to the alveolar bone must be
  understood. The fabrication of successful
  replacements can be accomplished in most cases
  only if the artificial teeth are placed in the
  same position that was occupied by the natural
  teeth they are replacing.
• The natural maxillary anterior teeth are inclined
  slightly forward of the alveolar bone. They
  contribute to the support of the upper lip
• With the canines providing support for the
  corners of the mouth. The mandibular incisors are
  also inclined forward and tend to support the
  lower lip. The maxillary posterior teeth are
  positioned slightly buccal to the alveolar ridge,
  when occluding with the mandibular molars the
  maxillary buccal cusps usually project 2 to 3 mm.
  beyond the buccal cusps of the mandibular teeth.
  The crowns of the lower posterior teeth are
  inclined inward

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• 2-relationship of occlusion rims to edentulous
  ridges
• The location and dimensions of the occlusion rims
  in relation to the edentulous ridge are basically
  the same as those for the crowns of the natural
  teeth that are to be replaced in their relation
  to the alveolar ridge. The occlusion rims simply
  replace the natural teeth both in dimension and
  in their relationship to anatomic structures.
  These relationships should be re-established by
  the occlusion rims even if resorption of the
  residual ridge has occurred following the removal
  of the natural teeth.

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3-fabrication technique and dimensions of
occlusion rim

• 1-base plate wax (modeling wax)
• A sheet of base plat wax is heated over
  approximately one half its length until the wax
  is soft and pliable. The soft wax is rolled to
  point to a point just short of unheated area. The
  wax is again heated and rolled until a soft roll
  has been formed. The soft wax roll is adapted to
  a bead of sticky wax that was previously applied
  to the recording base. The roll is further seated
  to the base. The roll is further seated to the
  base with spatula, with additional molten wax.

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• The edges of the roll are extended along the
  lateral surfaces to the border of the recording
  base. Additional wax is added to fill any voids
  in the contour of the rims. A heated broad bladed
  knife or plaster spatula is, used to quickly
  shape the labial surface of occlusion rim. The
  anterior surface should be inclined outward while
  the posterior surface is sloped slightly inward.
• A hot wax spatula is used to smooth the lingual
  surface and form a rim approximately 5mm wide in
  the anterior area and approximately 8-10mm in the
  posterior area.
• These basic dimensions are subjected to final
  chair side changes, since the dentist uses the
  rims to determine the proper vertical dimension,
  occlusal plane, facial support, as well as the
  midline of the arch, the length and width of the
  anterior teeth, the buccal eminence, the smiling
  (high) lip line, and the speaking(low) lip line.
• The occlusal surface of the occlusal rim must be
  smooth and flat. All surfaces of the rim should
  be smooth.

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2-the composition (compound
impression)

• 1-May be used and softend in warm water, molded
  into a back of the necessary size and placed
  into position.
• 2-a hot wax knife is used to adapt the edge, the
  surface is best smoothed with a sand
  paper.
• 3-the use of compound is indicated when it is
  desired to obtain more than one record of
  the occlusion, as with any type of fully
  adjustable articulator, or when gothic
  arch tracing is to be taken.

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3-plaster and pumice

• When a functional recording of mandibular
  movements is to be made by the patient chewing on
  bite rims, these should be made of a mixture of
  plaster and pumic. In this technique the patient
  goes through the movement of mastication with the
  bite blocks in occlusion and so produces the
  occlusal plane conforming to those movements. An
  acrylic base is the most satisfactory for this
  technique. The plaster is mixed with pumic equal
  parts of each, to facilate the grinding down in
  the mouth.

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• This plaster-pumic combination is mixed with
  water into a thick consistency and a roll of it
  is placed on to the base whilst the initial set
  is taking place. It can be smoothed with
  moistened fingers before setting is completed. A
  preliminary recording of vertical dimension is
  desirable which should be taken 3mm greater than
  finally required to allow for the reduction in
  grinding down in the mouth.
• These plaster rim should be made less than 24
  hours before they are required , otherwise the
  patient will have difficulty in grinding them
  down owing to the increased hardness of the
  plaster.